1. Field of the Invention
The invention relates to a magnetic resonance method for the volume-selective extraction of spectral information from an object containing a first type of nucleus and a second type of nucleus which is coupled to the first type of nucleus, the object being arranged in a steady, uniform magnetic field, the spectral information being extracted from magnetization transfer from one of the first and second types of nuclei to the other.
The invention also relates to a magnetic resonance imaging device for the volume-selective extraction of spectral information from an object containing a first type of nucleus and a second type of nucleus which is coupled to the first type of nucleus, which device comprises means for generating a steady, uniform magnetic field, transmitter means for transmitting RF electromagnetic pulses to the object arranged in the steady field, means for generating magnetic field gradients superposed on the steady field, and receiving and processing means for the magnetic resonance signals generated in the object, which processing means include programmed means and are operative to apply, by way of the transmitter means, pulses to the first and the second type of nucleus so that the spectral information is extracted from magnetization transfer.
2. Description of the Prior Art
A magnetic resonance imaging method and device of this kind are known from European Patent Application No. 0 347 990 which corresponds to U.S. Pat. No. 4,987,369. The cited Application describes a volume-selective polarization transfer sequence in which volume selection of a part of the object coincides with a polarization transfer sequence, three pulses of which are applied to a first type of nucleus via a first channel, while two pulses thereof, being at least partly coincident with the three pulses, are applied to a second type of nucleus via a second channel. The nuclei are, for example proton-coupled carbon atoms such as in a CH.sub.n system. Volume selection is achieved by application of slice-selective magnetic field gradients during application of the pulses.
Even though such a known method offers an improvement over, for example so-called DEPT sequences (Distortionless Enhancement by Polarization Transfer) preceded by volume selection such as VSE (Volume Selective Excitation), the known sequence still has drawbacks. This is because the transfer efficiency is highly dependent on correct adjustment of the excitation angle of the pulses to protons as well as .sup.13 C in, for example a CH.sub.n system. Accurate timing of the pulses is also a critical factor. For such sequences use is often made of a double surface coil having different RF profiles, so-called B.sub.1 profiles, for the proton fields and the .sup.13 C fields. The latter makes adjustment additionally difficult in practice. For in vivo measurements the efficiency of the magnetization transfer may be further affected by excitation angle variations due to local B.sub.1 inhomogeneities.